Many industrial processes require the equal distribution of heterogeneous flows to multiple receptors. For example in the electric utility industry, pulverized coal (“PC”) is transported through a pipe (duct) system that connects a grinding mill to one, or more, burners of a furnace. The PC is transported within the pipe system by a carrier gas, e.g., air. Thus, the heterogeneous flow, or stream, is made up of the PC and air (i.e., a two-phase flow or multi-phase flow). Ideally, one grinding mill is capable of supplying one or more such streams to multiple burners (receptors) of the furnace.
Unfortunately, as a stream moves through a long length of pipe, the solid particles in the stream tend to concentrate together in a pattern generally characterized as being in the shape of a rope strand. This phenomenon is commonly referred to as roping, or laning. As such, any attempt to further distribute, or split, a stream into multiple streams for transport to respective receptors seldom, if ever, yields equal amounts of PC going to each of the receptors. In other words, when roping occurs in a stream, splitting that stream into multiple streams results in a flow imbalance between the multiple streams. This flow imbalance is also compounded by unequal pressure drops across the coal pipes caused by non-identified pipe length and configurations. Resulting flow imbalances could be on the order of ±30% between the multiple streams.
Likewise, with respect to receptors fed by multiple sources, roping makes it difficult to combine the flows from these multiple sources such that each of the receptors are supplied with equal flows.
Various methods and devices have been utilized to obtain more uniform and homogenous two-phase flow through a fuel pipe system, as the flow travels from the coal mill to the furnace. Such methods and devices are implemented at different points downstream of the coal mill. One such method and device is a conventional adjustable orifice, as illustrated in FIG. 1. The conventional adjustable orifice can be implemented at any point along the furnace pipe system. Such an adjustable orifice comprises opposed gate boxes 120 and 121 located along a pipe or between pipes. The gate boxes include slidable gates 123 and 124, which can be adjusted to regulate the resistance to the flow of coal and a carrier gas flowing into the pipe 111 from pipe 110 by altering the opening between gates 123 and 124.
To increase the amount of coal and a carrier gas into the pipe 111, the gates can be retracted into the gate boxes 120 and 121. Conversely, to reduce the amount of flow through the pipe 111, the gates 123 and 124 can be positioned closer together.
The use of such an adjustable orifice has disadvantages. The adjustable orifice was initially designed for use in a single-phase flow. As shown in FIG. 1, if used in a two-phase system, once the flow passes through the gateway opening, coal eddies 125 are created from streams of coal, which are interrupted as they travel over the top edges 123-1 and 124-1 of the gates 123 and 124. Such eddies not only wear down the interior walls of the pipe, but leave piles of coal immediately outside the gates 123 and 124. Additionally, coal piles up within the gate boxes 120 and 121, unless a complicated sealing system is used, eventually making it difficult to retract the gates into the gate boxes. As a result such orifices are most effective when used in a vertical direction, in order to minimize coal pile-up downstream of the gates.